Flexible and slidable waveguide feed system for a radiating horn antenna

ABSTRACT

A radiating waveguide horn is provided having a hollow tubular portion and significantly broader radiating portion. The hollow tubular portion is adapted to coaxially receive therein a closely spaced rectangular waveguide feed structure. The waveguide feed structure is dimensioned to pass easily within the hollow tubular portion leaving a gap between the waveguide feed structure and the inner surface of the hollow tubular portion of the waveguide horn. A pair of elongated curved metal strips are fixed to one end of the waveguide feed structure with the metal strips generally extending along the length of said structure. The metal strips are configured and arranged relative to opposite walls of the waveguide feed structure so that the strips make flexible contact with the inner surface of the hollow tubular portion of said horn.

United States Patent Landry et al.-

[54] FLEXIBLE AND SLIDABLE WAVEGUIDE FEED SYSTEM FOR A RADIATING HORN ANTENNA [72] Inventors: Norman Richard Landry, Willingboro; Robert Jean Mason, Medford; William Hugh Schaedla, Medford Lakes; Willard Thomas Patton,

- Moorestown, all of NJ.

[73] Assignee: RCA Corporation [22] Filed: May 6, 1971 [21] Appl. No.: 140,887

[52] US. Cl. ..343/772, 343/778, 343/786, 343/787, 343/851, 343/862 [51] Int. Cl. ..H0lq 1/20, HOlq 13/02 [58] Field of Search ..343/85l, 862, 772-780, 343/786-787, 907; 333/98, 21, 24.1

[56] References Cited UNITED STATES PATENTS 3,324,423 6/1967 Webb ..333/2l [45] Oct. 10, 1972 Primary Examiner-Herman Karl Saalbach Assistant, Examiner-Marvin Nussbaum Attorney-Edward J. Norton [57] ABSTRACT A radiating waveguide horn is provided having a ho]- low tubular portion and significantly broader radiating portion. The hollow tubular portion is adapted to coaxially receive therein a closely spaced rectangular waveguide feed structure. The waveguide feed structure is dimensioned to pass easily within the hollow tubular portion leaving a gap between the waveguide feed structure and the inner surface of the hollow tubular portion of the waveguide horn. A pair of elongated curved metal strips are fixed to one end of the waveguide feed structure with the metal strips generally extending along the length of said structure. The metal strips are configured and arranged relative to opposite walls of the waveguide feed structure so that the strips make flexible contact with the inner surface of the hollow tubular portion of said horn.

6 Claims, 3 Drawing Figures PATENTEnnm 10 m2 3.698 Q 000 #vvavroas Norman 1?. Landry,

Robert J. Mason, William I]. Scbaedla & Willard 71 Patton Fin. ,5" 1%: f f1 4 TTORNEY FLEXIBLE AND SLIDABLE WAVEGUIDE FEED SYSTEM FOR A RADIATING HORN ANTENNA This invention relates to a waveguide feed system for a waveguide horn antenna.

In a phased array system using a plurality of horn type radiating elements and an associated phase shifter, the radiating horn element is usually permanently mounted on the array structure. The microwave feed system of the phased array, which may include the phase shifter as a part thereof, is usually removable for maintenance purposes. Due to the close spacing of the radiating elements in a phased array system and the configuration of the feed equipment associated with the phase shifter, physical access to the connection between the waveguide feed structure and the horn is very limited.

When the waveguide feed system also functions as a phase shifter section, the waveguide feed structure includes relatively high dielectric gyromagnetic materials such as garnets and ferrites. These materials are generally fragile and therefore the waveguide structure containing these materials cannot be rigidly attached to the horn, since to do so would cause the gyromagnetic material to break in response to thermal expansion or contraction stresses. Also, it is desirable to provide an air passage around the phase shifter to allow cooling thereof. In addition, from the microwave point of view, the outside of the waveguide feed structure housing and the inside of the horn effectively cooperate to form a section of coaxial line. Propagation of reflected electromagnetic signal waves along this coaxial line is undesired and must be prevented.

As herein described, there is provided a radiating waveguide horn having a hollow tubular conductive portion adapted to receive therein a slidable waveguide feed structure. This slidable waveguide feed structure is dimensioned to pass easily within the hollow tubular conductive portion of the horn. A pair of elongated conductive metal strips are fixed to opposite sides of the waveguide feed structure atone end of the feed structure. The metal strips have a curved transverse configuration so arranged that when the waveguide feed structure is inserted into the hollow tubular conductive portion of the horn the metal strips act electrically as a flexible microwave choke at microwave frequencies and mechanically to resiliently hold the waveguide feed structure to the horn.

A further description follows in conjunction with the accompanying drawing, wherein:

FIG. 1 is an isometric drawing of an assembled waveguide feed structure and horn, with a portion of the horn structure removed for illustration;

FIG. 2 is a cross section of the feed system and the horn assembly taken through the 2-2 plane in FIG. 1; and

FIG. 3 is a side view of a portion of the sliding waveguide feed structure.

Referring to FIG. 1, there is illustrated a radiating horn antenna 11 having slidably positioned therein the waveguide feed structure 13. The horn antenna 11 is a rectangular horn with a flare in the plane of the magnetic field. This type of horn is commonly referred to as an H-plane sectoral horn. Portion 15 of the horn antenna 1 1 assumes this configuration. The horn antenna 11 has a hollow tubular portion 17 which has an aperture 17A therein adapted to receive the rectangular waveguide feed structure l5.

Referring to FIG. 2, there is illustrated in cross section the hollow tubular portion 17 of the horn antenna 11 with the waveguide feed structure 13 therein. The waveguide feed structure 13 is made up of a dielectrically loaded rectangular waveguide section 13A and a symmetrically stepped impedance matched section 13B. The waveguide feed structure 13 has the walls dimensioned slightly smaller than the rectangular aperture 17A of the hollow tubular portion 17 of the horn antenna 11 to allow easy placement of the waveguide feed structure 13 into the horn antenna 11. The portion 13A of the waveguide feed structure 13 is adapted to propagate signals at the frequency of interest in the TE mode. The section 13A of waveguide feed structure 13 includes two broad walls 14 and 16 and two narrow walls 18 and 20. The section 13B of the waveguide feed structure 13, when in the operating feed position extends into the portion 15 of the horn antenna 11. As shown in FIGS. 1 and 3, the section 13B is made up of an extension of the broad walls 14 and 16 and a symmetrical step transformer comprising a first relatively thin dielectric spacer 41 and a relatively shorter broad dielectric spacer 43.

In addition to acting as a waveguide feed for the horn antenna 11, the waveguide feed structure 13 may also act as a phase shifting element for the signals being propagated to the horn antenna 11. When several such horn antennas are used to provide a phased array antenna, the phase shift provided by each of these waveguide phase shifting feed structures is used to control the combined far field radiation pattern of the phased array antenna. In such a phase shifting arrangement, the waveguide feed structure 13 may have a centrally positioned toroid 21 therein which extends a given length dependent upon the desired phase shift along the waveguide feed structure 13. The toroidal member 21 shown in the drawing is made of gyromagnetic material.

The term gyromagnetic material refers to both ferromagnetic and ferrimagnetic materials. A more complete description of such materials can be found in chapters 2 and 3 of Microwave Ferrites and Ferrimagnetics by Lax and Button, published by McGraw-I-Iill USA.

A biasing wire 47 is placed within the aperture 23 of the toroid 21 and extends along the longitudinal length of the toroid 21. The biasing wire 47 exits the toroid 21 at the horn end and passes along the outside wall 18 of the waveguide feed structure 13. The opposite ends of the wire 47 are connected to the opposite terminals of a dc. control source 51 (see FIG. 1

Upon the application of a dc. pulse along this wire, the toroid 21 is caused to be latched or to be magnetized in one sense to provide a given amount of phase shift for signals propagating in one direction along the waveguide feed structure 13. The portion 17 of the horn 11 has a longitudinally extending groove 19 therein adapted to easily pass the wire 47 as the feed structure 13 is slid into the horn 11. The wire 47 has adhesive thereon to hold it to the wall 18 in aligned position to the groove 19.

The cross sectional dimension of the waveguide feed structure 13 is reduced by the placement of the relatively high dielectric constant gyromagnetic material in the waveguide feed structure 13. The dielectric constant of such a materialmay be l5, for example.

A pair of curved elongated metal strips 25 and 27 are fixed to the waveguide structure 13. One end of curved elongated metal strip 25 is fixed by a pair of rivets to extended broad wall 14 at end 26 of the waveguide feed structure 13. One end of curved elongated metal strip 27 is fixed by a pair of rivets to extended broad wall 16 at end 26 of the waveguide feed structure 13. These strips 25 and 26 are fixed to the waveguide feed structure 13 such that their lengthwise axis extends along the broad walls 14 and 16 respectively of the waveguide feed structure 13 toward end 28. Referring to FIG. 3, it is seen that these metal strips 25 and 27 extend alongthe lengthwise axis of the waveguide feed structure 13 with the metal strips being shaped or biased such that, as they extend away from the fixed end 26, the metal strips 25 and 27 tend to increase their spacing from the broad walls 14 and 16.

Referring to FIG. 2, it can be seen that the metal strips are further shaped such that across the width of the strips 25 and 27 in the direction which is transverse to the direction of propagation of signals along the waveguide feed structure 13 the strips are curved with the apex of the curve or are at the cross sectional center of the metal strips and extending away from the walls of the waveguide feed structure. The curve of the strips is such that when the waveguide feed structure 13 is placed in the portion 17 of the horn, the apex 31 of the strip 25 and the apex 32 of the strip 27 touch the portion 17 of the horn. The cross sectional edges 35 and 36 of strip 25 touch the broad wall 14 of the waveguide feed structure 13 and the cross sectional edges 37 and 38 of strip 27 touch the broad wall 16 of the waveguide feed structure 13.

From a microwave point of view, the outside of the waveguide feed structure 13 and the inside of the ho]- low tubular portion 17 form a coaxial line. Propagation of electromagnetic waves along this coaxial line is prevented by the flexible metal strips 25 and 27. The impedance of this coaxial line section is about 1 ohm and the strips 25 and 27 maintain the required short circuit with variations in alignment and insertion.

Matching of the waveguide feed structure 13 to the horn antenna 11 for low VSWR (voltage standing wave ratio) must compensate for the irregular waveguide walls. This can be accomplished by the symmetrically stepped transformer section 133. The transformer section 133 comprises an extension of the broad walls 14 and 16 only into the flared portion of the horn antenna 11. A symmetrically stepped body of ceramic material having a narrow portion 41 and a relatively broad portion 43 is spaced between the extended broad walls 14 and 16 to form a waveguide-to-horn matching section.

It can be seen that the structure described above provides a flexible and slidable waveguide feed system-tohorn junction. The flexible metal strips 25 and 27 allow the waveguide feed structure 13 to be loosely inserted into the horn with mechanical and electrical contact provided by these metal strips. Clearance between the waveguide feed structure 13 and the hollow tubular portion 17 of the horn 11 is less than the height-of the are formed by the transverse curve of the strips 25 and 27. When the waveguide section is inserted in the horn, the hollow tubular portion 17 of the horn contacts the strips 25 and 27 at the high point (31 or 32) of the are or curve and flattens the strips 25 and 27 bular portion 17 of the horn.

A small lateral amount of motion between the waveguide feed structure 13 and the tubular portion 17 of the horn is possible, since the height of the arc in the strips is sufficient to assure contact even though the waveguide feed structure 13 is inserted in such a way as to force it against one of the other walls of the horn. The elastic properties and dimensions of the strips give them the characteristic of springs in that they can be fully deflected within the limits of the configuration and will return to the original shape without permanent deformation. The curved metal strips, by being fixed only tovone of the four edges of the waveguide feed structure 13, eliminate the possibility of buckling of the strips due to differential thermal expansion between the strips and the waveguide feed structure 13.

Because of the flexible nature of the junction, this design minimizes the stresses on the gyromagnetic material in the waveguide feed structure 13. Because of the spacing between the tubular portion 17 of the horn and the waveguide feed structure 13, the design allows air to flow to pass around the waveguide feed structure to allow cooling thereof. Further, this design allows the multiple simultaneous connections associated with a system of such horns and feed systems to be made in an inaccessible area with only a small insertion of the waveguide feed structure into the horn.

What is claimed is:

1. A resiliently and slidably mounted waveguide feed for coupling electromagnetic signal waves to a radiating waveguide horn antenna having a first hollow tubular conductive portion and waveguide radiating portion comprising, in combination:

a waveguide structure dimensioned to easily pass within said hollow tubular portion of said horn, leaving a gap therebetween,

. a first of a pair of elongated conductive metal strips fixed near one end of said structure to one wall of said structure in a manner so that said first. strip extends along a portion of the length of said one wall,

a second of said pair of elongated conductive metal strips fixed near said one end of said structure to a second wall opposite said one wall of said waveguide structure in a manner so that said second strip extends along a portion of the length of said second wall,

said metal strips having a curved transverse configuration that extends away from said structure so that when said waveguide structure is inserted into the tubular portion of the horn, said metal strips act electrically as a flexible choke as to said electromagnetic signal waves and mechanically to flexibly secure said waveguide structure to the hollow tubular portion of the horn.

2. The waveguide feed as claimed in claim 1, wherein said waveguide structure includes a body of relatively high dielectric constant material.

3. The waveguide feed as claimed in claim 2, wherein the dielectric constant of said material is at least 15.

4. The waveguide feed as claimed in claim 2, wherein said dielectric material comprises gyromagnetic material.

5. The waveguide feed as claimed in claim 4, wherein said gyromagnetic material is in the form of a toroid.

6. In combination:

against the tua rectangular waveguide horn antenna having a first hollow tubular rectangular waveguiding portion and a second waveguide radiating portion adjacent to said first portion,

a waveguide structure adapted for coupling eleca first of a pair of elongated conductive metal strips fixed at one end to the extended portion of one of said broad walls of said waveguide structure in a manner so that the first strip extends along a portion of the length of said one of said broad walls, and

a second of said pair of elongated conductive metal strips fixed at one end of the extended portion of the second of said broad walls of said waveguide structure opposite said one of said broad walls in a manner so that the second strip extends along a portion of the length of said second of said broad walls, said metal strips having a curved transverse configuration that extends away from said waveguide structure so that when said waveguide structure is inserted into the tubular portion of the horn, said metal strips act as a flexible choke as to coupled electromagnetic signal waves and act to resiliently secure the waveguide structure to the first portion of the horn,

said waveguide structure being positioned within said horn so that said first section of said waveguide structure is aligned with said first portion of said horn and said second portion of said waveguide structure is aligned with the second portion of said horn. 

1. A resiliently and slidably mounted waveguide feed for coupling electromagnetic signal waves to a radiating waveguide horn antenna having a first hollow tubular conductive portion and waveguide radiating portion comprising, in combination: a waveguide structure dimensioned to easily pass within said hollow tubular portion of said horn, leaving a gap therebetween, a first of a pair of elongated conductive metal strips fixed near one end of said structure to one wall of said structure in a manner so that said first strip extends along a portion of the length of said one wall, a second of said pair of elongated conductive metal strips fixed near said one end of said structure to a second wall opposite said one wall of said waveguide structure in a manner so that said second strip extends along a portion of the length of said second wall, said metal strips having a curved transverse configuration that extends away from said structure so that when said waveguide structure is inserted into the tubular portion of the horn, said metal strips act electrically as a flexible choke as to said electromagnetic signal waves and mechanically to flexibly secure said waveguide structure to the hollow tubular portion of the horn.
 2. The waveguide feed as claimed in claim 1, wherein said waveguide structure includes a body of relatively high dielectric constant material.
 3. The waveguide feed as claimed in claim 2, wherein the dielectric constant of said material is at least
 15. 4. The waveguide feed as claimed in claim 2, wherein said dielectric material comprises gyromagnetic material.
 5. The waveguide feed as claimed in claim 4, wherein said gyromagnetic material is in the form of a toroid.
 6. In combination: a rectangular waveguide horn antenna having a first hollow tubular rectangular waveguiding portion and a second waveguide radiating portion adjacent to said first portion, a waveguide structure adapted for coupling electromagnetic waves having a first section and an adjacent second section, said first section having a pair of broad walls and a pair of narrow walls dimensioned and arranged to form a rectangular waveguide that can easily pass within said first rectangular waveguide portion of said horn leaving a gap therebetween, said second section of said waveguide structure including an extension of the pair of broad walls of said waveguide structure, a first of a pair of elongated conductive metal strips fixed at one end to the extended portion of one of said broad walls of said waveguide structure in a manner so that the first strip extends along a portion of the length of said one of said broad walls, and a second of said pair of elongated conductive metal strips fixed at one end of the extended portion of the second of Said broad walls of said waveguide structure opposite said one of said broad walls in a manner so that the second strip extends along a portion of the length of said second of said broad walls, said metal strips having a curved transverse configuration that extends away from said waveguide structure so that when said waveguide structure is inserted into the tubular portion of the horn, said metal strips act as a flexible choke as to coupled electromagnetic signal waves and act to resiliently secure the waveguide structure to the first portion of the horn, said waveguide structure being positioned within said horn so that said first section of said waveguide structure is aligned with said first portion of said horn and said second portion of said waveguide structure is aligned with the second portion of said horn. 